I would not rebuild it with an NOS kit. Rust? Pitting? decayed seals or whatever?
I sent my 216 water pump to The Frying Dutchman (Come for the freak. Stay for the food) a year and a half ago. So far, so good. You can see his rebuild procedure on Youtube where he is coincidentally rebuilding a Chevy 216 water pump.
He's been around for decades and has a good reputation in the antique Cadillac community.
Then and Now Automotive will also rebuild your pump and I believe they sell kits to do it yourself. They did a great job on my fuel pump and have a good reputation as rebuilders of many antique car parts (balancers, motor mounts, fuel pumps, etc)
The pumps are so easy to install and remove, I'm not sure I would mess with it if it isn't leaking and if there is no play in the bearing. You could take the rear cover off and inspect the vanes on the impeller and look for corrosion. Have you had overheating problems that point to possible pump failure?
If all is well, button it up and reuse it.
Water pump rebuilder and seller of antique water pumps for all makes and models. Services Europe and USA
Flying Dutchman
Wade Jenezon, 650 Upper River Rd
Gold Hill, OR 97525 USA
1-888-595-1110 Outside the U.S., 1-541-450-2277
http://water-pump-rebuilders.com/Then and Now Automotive
447 Washington St
Weymouth, Ma 02188
Ph: 781.335.8860
Fax: 781.335.1925
https://www.then-now-auto.com/
